Zinc plating

ABSTRACT

A NON-CYANIDE ZINC ELECTROPLATING BATH CONTAINS AN ORGANIC COMPOUND WHICH CONTAINS WITHIN THIS STRUCTURAL FORMULA A SULFONIC ACID AND A SULFUDE, MERCAPTO OR POLYSULFIDE GROUP. THE ADDITIVES ARE INTRODUCED TO OBTAIN A BRIGHT ZINC PLATE, AS WELL AS TO OBTAIN A LEVELING EFFECT.

3,748,237 ZINC PLATING Hans Gerhard Creutz, Westiand, Mich., assiguor toOxy Metal Finishing Corporation, Warren, Mich. No Drawing. Filed July14, 1971, Ser. No. 162,690 Int. Cl. C23b 5/12 US. Cl. 204-55 R 24 ClaimsABSTRACT OF THE DISCLOSURE A non-cyanide zinc electroplating bathcontains an organic compound which contains within this structuralformula a sulfonic acid and a sulfide, mercapto or polysulfide group.The additives are introduced to obtain a bright zinc plate, as well asto obtain a leveling effect.

This invention relates to an improved composition and process for theproduction of bright zinc electrodeposits and more particularly, relatesto compositions and processes for forming bright zinc electrodepositsfrom non-cyanide zinc electroplating baths.

Heretofore, various processes have been utilized for theelectrodeposition of zinc to provide both corrosion resistant anddecorative coatings, praticularly on ferrous metals, such as iron andsteel. ln general, the zinc electroplating baths have been either acidzinc baths, which are generally operated in a pH range of from about 3to 5, and alkaline zinc baths, which are generally operated in a pHwithin the range of from about to 14. Although the acid zinc platingbaths are more inexpensive to operate, because of their relatively poorthrowing power, their use has been largely restricted to the plating ofrelatively simple shapes, such as steel strip, pipe, wire, and the like,in which the plating is carried out over a relatively narrow currentdensity range. Additionally, because of the corrosive nature of the acidzinc baths, corrosion resistant linings such as rubber, lead, ceramics,synthetic resins and the like, must be used in the plating tanks. Forthese reasons, the acid zinc plating baths have not been widely used.

The alkaline zinc plating baths have commonly been of two types, thecyanide-free baths, which contain sodium zincate, and the moreconventional bright zinc baths which contain sodium cyanide. The sodiumzincate baths, however, have a relatively low efiiciency and producesoft-spongy electrodeposits. Moreover, even with various additives, thezinc deposits produced are not as bright as those obtained from cyanidebaths and, hence, there has been little commercial use of such baths.

With the alkaline cyanide zinc plating baths, however, generallyacceptable electrodeposits are obtained, the baths are stable andrelatively easy to control and the cyanide-containing solution is notcorrosive to ferrous metal plating tanks. Accordingly, such baths havebeen widely used commercially. Nothwithstanding, this widespreadcommercial acceptance, however, in recent years, there has been anincreasing awareness that these plating baths containing sodium cyanideconstitute both a health hazard to operating personnel and a source ofindustrial pollution. Accordingly, and particularly because of theincreased expense encountered in the installation and operation of thespecial processing equipment to overcome the waste disposal problem,significant numbers of platers having discontinued the use of zinc andswitched to other metals as substitutes.

It is, therefore, an object of the present invention to provide animproved bright zinc plating bath which is free of cyanide.

Another object of the present invention is to provide a cyanide-freebright zinc plating bath which was excellent throwing power and willstill produce a smooth, bright, adherent zinc deposit.

United States Patent 0 A further object of the present invention is toprovide an improved process for the electrodeposition of a smooth,bright, adherent zinc deposit from a cyanidefree zinc plating bath.

These and other objects will become apparent to those skilled in the artfrom the description of the invention which follows.

Pursuant to the above objects, the present invention is directed to anaqueous cyanide-free zinc electroplating bath, which contains asbrightening additives, an organic compound wherein the molecule containsa sulfonic acid group and a sulfide or mercapto, or polysulfide grouphereinafter referred to as brightener #1. More precisely, thebrightening additives are of the structure:

wherein: n is from 1 to 3; f is from 0 to 3; f is from 0 to 3;

R and R independently may be hydrogen, alkyl of 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms, cyclo hexyl, phenyl, benzyl, naphthyl,thiazolyl or benzothiazolyl, providing that f, and f when added togetheris at least one and that when R is hydrogen, 1, is 0 and when R; ishydrogen, f is 0.

Some compounds which are brightener #1 are of the following structures:(1) HS(CH -'SO H prepare by reacting sodium sulfide with propanesultone. (2) HO S(CH -S-S(CH SO H prepare by reacting #1 with hydrogenperoxide.

Additional brightening additives may be added to supplement the activityof the aforementioned additive such 3 as those described in US. 'Ser.No. 20,855, filed Mar. 18, 1970. In that case, brightening additives aredescribed containing a combination of linear polyether and aheterocyclic nitrogen compound. These baths may also contain an organicchelating agent which have been found to produce bright, lustrous zincelectrodeposits over a wide range of operating conditions.

More specifically, the baths of the present invention are aqueous,cyanide-free zinc electroplating baths having a pH of from about 7.0 to9.6, preferably 7.5 to 8.0 and containing the aforementioned brightener#1 in amounts sufficient to produce a zinc electrodeposit havingimproved brightness. These baths are aqueous solutions of zinc salt,such as zinc sulfate, zinc chloride, zinc fiuo borate, or the like.Additionally, the bath may also contain ammonium chloride, which hasbeen found to improve the bath conductivity and throwing power.Desirably, these baths contain the zinc in an a mount within the rangeof about 10 to 30 grams/liter being preferred. Additionally, whereammonium chloride is included in the bath it is desirably present inamounts within the range of about 20 to 300 grams/liter, with amountswithin the range of about 100 to 200 grams/liter being preferred.Moreover, compounds such as ammonium hydroxide, and hydrochloride acidmay also be included in the zinc plating baths in amounts which willprovide the desired pH of the bath. Accordingly, the specific amountsused will vary depending upon the specific make-up of the particularzinc plating bath which is being used.

The organic sulfo and sulfide compound which is added as a brighteningadditive, is present in amount from about 0.002 to about 10 grams/literwith an amount within a range of about 0.01 to about 1.0 gram/literbeing preferred.

As additional brightening additives, it has been found that thecyanide-free electroplating baths of the present invention may alsocontain at least a linear polyether and a heterocyclic nitrogencompound. Desirably, the polyether compound is present in the bath in anamount within the range of about 0.2 to 20 grams/liter, with an amountwithin the range of about 0.5 to grams/liter being preferred. Thepolyether compounds which have been found to be suitable for use in theplating baths of the present invention are linear, mono or difunctionalpolyethers which are substantially free of said chains which terminatein a functional group, such as OH group. Suitable linear polyethers ofthis type include the difunctional polyethers, such as the polyglycols,exemplary of which are the polyethylene glycols, polypropylene glycols,mixed polymers of polyethylene and polypropylene glycol, and the like,as well as the monofunctional linear polyethers, such as the ethoxylatedalkyl phenols, ethoxylated fatty alcohols, and the like. Typically,these linear compounds will have a molecular weight within the range ofabout 500 to 1,000,000. In the case of the monofunctional linearpolyethers such as the ethoxylated alkyl phenols, these may contain upto about 18 carbon atoms in the alkyl group and up to about 50 moles ofethylene oxide. Of the various linear polyethers which are suitable foruse in the present electroplating bath, the polyethylene glycols havinga molecular weight of from about 1000 to 100,000 and the condensationproducts of nonyl phenol with about 30 moles of ethylene oxide, havebeen found to be preferred. It is to be appreciated, however, that thesematerials are merely exemplary of the linear polyethers which may beused and are not to be taken as a limitation on these materials.

The heterocyclic nitrogen compound additives, which are used inconjunction with the polyether materials, are desirably present in thepresent zinc electroplating bath in amounts Within the range of about 2milligrams to grams/liter, with amounts within the range of about 10 to100 milligrams/liter being preferred. These additive materials arebath-soluble quaternary nitrogen compounds which contain at least onesubstituting group selected from carboxylic esters, carboxamides,carboxy, and nitrile groups which have been quaternized with agents suchas benzyl chloride, allyl bromide, methyl or ethyl and propylnicotinate; for example, n-benzyl-3 alkyl carboxylate pyridiniumchloride or the quaternary resulting from reacting benzyl chloride andnicotinic acid. The suitable heterocyclic nitrogen compounds of thistype are described in detail in U.S. Pat. 3,318,787. Although in thispatent, these compounds are disclosed as producing smooth, bright zincdeposits when added to alkaline cyanide zinc electroplating baths,suprisingly it has been found that when used alone in the non-cyanidezinc electroplating baths of the present invention, they have littleeifect. It is only when these heterocyclic nitrogen compounds are usedin conjunction with the linear polyether materials that full bright zincelectrodeposits are obtained from the non-cyanide baths.

In addition to the linear polyether material and the heterocyclicnitrogen compounds, in many instances it has also been found to bedesirable to include in the plating baths an organic chelating orsequestering agent to help prevent the formation of zinc hydroxide.These chelating agents are used in amounts suflicient to chelate thezinc in the bath, and hence, the specific amounts used will vary in eachinstance, depending upon the composition of the bath. Typically,however, they are present in amounts up to about 250 grams/liter, withamounts within the range of about 10 to 150 grams/liter being preferred.Exemplary of the Various suitable chelating agents which may be used areethylene diamine tetraacetic acid, nitrilotriacetic acid, ethylenediamine tetraethanol, citric acid, and the like, including the varioussalts of these compounds.

In formulating the zinc electroplating baths of the present invention,the various additive materials may be added separately to the bath inamounts which will provide the desired concentration of these componentsin the bath. Preferably, however, an aqueous concentrate composition isutilized which contains all of the desired additive material in theproper ratio and proportion to each other so as to provide the desiredconcentration of these materials in the bath. Thus, a suitable additiveconcentrate composition for use in formulating the zinc electroplatingbaths of the present invention may contain the following components inthe amounts indicated:

Organic chelating agent (when present at least 10 g./l.) 0250 Brightener#1 0.002-10 In utilizing the plating baths of the present invention, thebaths may be operated at temperatures up to about 60 degrees Centigrade,with temperatures in the range of about 15 to 30 degrees centigradebeing preferred. The pH of the plating bath during the operation may beWithin the range of about 7.0 to 9.6 with pHs from about 7.5 to 8.0being preferred. Desirably, the average cathode current densities usedwill be within the range of about 5 to amps/square foot being preferred.Desirably, the average cathode current densities used will be within therange of about 5 to 100 amps/square foot, with average current densitiesof from about 10 to 50- amps/square tfoot being preferred. Thus, it isto be appreciated that the plating baths of the present invention may beused in various plating operations, including both barrel plating andrack plating processes.

In order that those in the art may better understand the presentinvention and the manner in which it may be practiced, the followingspecific examples are given. In these examples, unless otherwiseindicated, parts and percent are by weight and temperatures are indegrees centigrade. It is to be appreciated, however, that these aremere- 1y exemplary of the present invention and are not to be taken aslimitation thereof.

EXAMPLE 1 A cyanide-(free electroplating bath was formulated containingthe following components in the amounts indicated:

Component: Amounts Zinc chloride grams/liter 50 Ammonium chloride do 200Tetraethanol ethylene diamine do.. 50 Ammonium hydroxide (29% by weight)milliliters/ liter- 25 Polyethylene glycol (molecular weight 4000)grams/liter 40 Ethylnicotinate-benzyl chloride quaternarymilligrams/liter 50 dO 20 Using this plating bath, at a pH of 8.0, abent J-shaped steel cathode was plated for 20 minutes at a currentdensity of 30 amps/ square foot and a uniform full bright zincelectro-deposit was obtained.

EXAMPLE 2 A cyanide-free electroplating bath was formulated containingthe following components in the amounts indicated:

Component: Amounts Zinc chloride grams/liter 30 Ammonium chloride do 220Ammonium hydroxide (29% by weight) milliliters/liter -80 Polyethyleneglycol (molecular weight 100,000)

grams/liter" 1O Isopropyl nicotinate-benzyl chloride quaternarymilligrams/liter 30 With this bath, at a pH of 8.2, and an averagecurrent density of 20 amps/square tfoot, uniform full bright zincelectrodeposits were obtained, as in Example 1.

EXAMPLE 3 A cyanide-free electroplating bath Was formulated containingthe following components in the amounts indicated:

Component: Amounts Zinc chloride grams/liter 21 Ammonium chloride do 125Nitrilotriacetic acid .do 35 IGEPALCO 880 (trademark for nonyl phenolcontaining 30 molecules ethylene oxide, a product of General Aniline &Film do '10 Ethyl nicotinate quaternized with benzyl chloride mi1ligrams30 The bath was ran at a pH of 8.

Cathode deposits from such baths had a tendency to have a dull, roughplate at current densities higher than about 20 amps/square foot. When asimilar bath had added 50 milligrams/liter of mercapto propane sulfonicacid thereto the high current density plate is of a better quality aswell as the overall leveling and brightness was improved.

In a similar manner, the compound of the formula, using 30 milligrams/liter gave results equivalent to mercapto propane sulfonic acid,

6 EXAMPLE 4 In a manner similar to mercapto propane sulfonic acid ofExample 3, the compound of the following formula gave equivalentsatisfactory results using 0.1 gram/liter.

What is claimed is:

1. An aqueous zinc electroplating bath comprising as a source of zincions, a zinc salt selected from a group consisting of zinc sulfate, zincchloride, and zinc fiuoborate and as a brightening agent in amountssufiicient to produce a zinc electrodeposit of improved brightness, acompound of the formula:

wherein n is from 1 to 3; f is from 0 to 3; f is from 0 to 3; R and Rare independently selected from the group consisting of hydrogen, alkylof 1 to 6 carbon atoms, cyclo hexyl, phenyl, benzyl, naphthyl, thiazolyland benzothiazolyl, providing that f and f when added together is atleast one and that when R is hydrogen, f is 0 and when R; is hydrogen, fis 0, wherein the bath has a pH of from about 7.0 to 9.6 and alsocontains a linear polyether in an amount within the range of 0.2 to 20grams/ liter and a heterocyclic nitrogen compound present in an amountwithin the range of about 0.002 to 10 grams/liter.

2. The bath of claim 1 wherein the bath also contains a metal chelatingagent present in an amount up to 250 grams/liter.

3. The bath of claim 1 wherein zinc chloride is the source of zinc inthe bath.

4. The bath of claim 1 wherein n is 1.

5. The bath of claim 1 wherein n is 2.

6. The bath of claim 1 wherein R is alkyl of 1-6 carbon atoms.

7. The bath of claim 1 wherein R is hydrogen.

8. The bath of claim 1 wherein R is phenyl.

9. The bath of claim 1 wherein f and f total 2.

10. The bath of claim 1 wherein R is benzothiazolyl.

11. The method of depositing a smooth, adherent, bright zinc depositwhich comprises electrodepositing zinc from an aqueous cyanide freeelectroplating bath as claimed in claim 1.

12. The method as claimed in claim 11 wherein the bath also contains ametal chelating agent present in an amount up to 250 grams/liter.

13. The method as claimed in claim 11 wherein zinc chloride is thesource of zinc in the bath.

14. The method as claimed in claim 11 wherein n is 1.

15. The method as claimed in claim 11 wherein n is 2.

16. The method as claimed in claim 11 wherein R is alkyl of 1-6 carbonatoms.

17. The method as claimed in claim -11 wherein R is hydrogen.

18. The method as claimed in claim 11 wherein R is phenyl.

19. The method as claimed in claim 11 wherein f and f total 2.

20. The method as claimed in claim 11 wherein R is benzothiazolyl.

21. An aqueous zinc electroplating bath comprising as a source of zincions, a zinc salt selected from the group consisting of zinc sulfate,zinc chloride and zinc fluoborate and as a brightening agent in anamount sufiicient to produce zinc electrodeposit of improved brightness,a compound selected from the group consisting of and --O3SR1S--SRZ SO3Whfein R1 and R2 are independently selected from the group consisting ofalkyl of 1 to 6 carbon atoms; wherein the bath has a pH from about 7.0to 9.6 and also contains a linear poiyether in an amount within therange of 0.2 to 20 grams/liter and a nitrogen heterocyclic compoundpresent in the amount within the range of about 0.002 to 10 grams/liter.

22. The bath of claim 21 wherein the sulfonate compound is present in anamount ranging from about 0.002 to 10 grams/liter.

23. The bath of claim 22 wherein the bath also con- References CitedUNITED STATES PATENTS 2,849,351 8/1958 Gundel et ai. 20455 R X 3,023,1502/1962 Wilhnund et a1. 204-55 R X 2,830,014 4/1958 Gundcl et a1. 204-55X F. C. EDMONDSON, Primary Examiner US. Cl. X.R.

l5 204Dig. 2

